The present invention relates to data storage systems, and more particularly, this invention relates to a system for creating a single library image from multiple independent tape libraries.
In magnetic storage systems, data is read from and written onto magnetic recording media utilizing magnetic transducers commonly. Data is written on the magnetic recording media by moving a magnetic recording transducer to a position over the media where the data is to be stored. The magnetic recording transducer then generates a magnetic field, which encodes the data into the magnetic media. Data is read from the media by similarly positioning the magnetic read transducer and then sensing the magnetic field of the magnetic media. Read and write operations may be independently synchronized with the movement of the media to ensure that the data can be read from and written to the desired location on the media.
The largest tape archives in the world, if they were to store all the data that the users demanded, would use more tape cartridges than there are available, e.g., these systems would exceed the maximum tape cartridge counts of the largest tape libraries offered in the market. However, the storage demands of these archives are met by using multiple tape libraries. The most cost-effective way to implement multiple tape libraries is to physically connect these multiple libraries via a “pass-thru” which is capable of carrying one or more tape cartridges between the libraries to deal with access “hot spots.” An access hot spot is a term which describes a situation where one library experiences a peak in access demand for the tape cartridges stored therein. In these situations, the pass-thru is utilized to offload a portion of the assigned work to tape drives in another, under-utilized and connected library(ies).
The aggregation of these connected libraries then creates a “single library image” which can be utilized by higher level applications, rather than relying on a trying to deal with a plurality of library images, numbering N. In the past, the pass-thru technology has been limited to point-to-point connection and cartridge movement between established pairs of libraries. When larger images are being used, if the demand increased on both libraries of a pair, to lessen the load, a tape cartridge may be moved through one or more intermediary libraries to arrive at an under-utilized library. These may be visualized as the tape equivalent of “connecting flights” that are made from a source library, through intermediary library(ies), and finally arriving at the destination library. Therefore, in order to speed up each transfer between libraries and also to support a much higher degree of parallelism in the system, a simple cost-effective method and/or system capable of direct access to the plurality of tape libraries would be very beneficial.